The present invention relates to a paint spray booth and more particularly to a system for controlling a plurality of paint sprayers operating within the paint spray booth.
A paint spray apparatus for painting a succession of articles, for example vehicle bodies, generally includes a paint spray booth installed in a clean room. The paint spray booth includes a plurality of paint sprayers having paint spray heads such as rotary bell atomizers mounted on the end of a paint spray arm. Typical paint sprayers have up to nine axes and a corresponding number of servo motors. For example, a four-axis paint sprayer includes four servo motors for moving the paint spray arm vertically, extending the paint spray arm horizontally, tilting the paint spray head on the end of the paint spray arm, and driving a pump to supply paint to the paint spray head. Each of the servo motors in each of the paint sprayers is controlled by a servo drive mounted in a motion panel located outside the clean room.
An operater enters information, such as the model of the vehicle body and color to be painted, into a computer controller outside the clean room. This information is sent to one or more motion cards. For the rest of the painting cycle (one vehicle body), the motion cards send signals to each servo drive indicating desired rates and directions of motion for each axis. Cables connect the motion card to IDC connectors mounted on the motion panel. Another set of cables connect the IDC connectors to each of the servo drives. Yet another set of cables from the servo drives to the IDC connectors to the motion card provide feedback from the servo drives to the controller.
Each of these servo drives provides a control signal to its corresponding motor through a plurality of wires connected to plugs mounted on the motion panel. From the motion panel, cables connect to plugs mounted on an explosion-proof box on the paint sprayer. The length of these cables, up to 50 meters, will vary for each sprayer because each sprayer is a different distance from the motion panel. Similarly, feedback signals from the motor pass through the explosion-proof box to another set of plugs, where cables of varying length up to 50 meters carry the signals to the plugs mounted on the motion panel, where a plurality of wires carry the feedback signals to the servo drive.
For each axis of each paint sprayer, three limit switches are typically used to provide additional feedback to the computer. The limit switches indicate overtravel in each direction on each axis and indicate a "home" position on that axis. The signals from the limit switches are carried to a junction box mounted on each paint sprayer. Cables connect plugs on a junction box on each paint sprayer to plugs mounted on the motion panel. In the motion panel, intrinsic safety barriers are connected between the plugs on the motion panel and IDC connectors. Ribbon cables carry the feedback signal from the IDC connectors to the motion card.
Each paint sprayer further includes a plurality of transducers for controlling functionality of the bell paint spray head. The transducers are mounted in a transducer panel on or near each paint sprayer. A first transducer controls the shape of the spray from the rotary bell paint spray head. A second transducer controls the rotation speed of the of the rotary bell paint spray head. A third transducer controls the supply of paint to the paint spray head. A dispatcher in each transducer panel receives a control signal from the computer along a cable up to 50 meters in length. The dispatcher then sends a control signal to each of the transducers. However, these transducers and dispatchers are expensive.
In the known system, the installation time and cost are greatly increased by the need to size and connect numerous wires, cables, plugs and connectors. Cables between the motion panel and each sprayer must be individually sized because each sprayer is a different distance from the motion panel and computer. The paint is potentially explosive and each connection point for each wire provides a possible source of a spark. Further, each connection between the computer and the sprayers is a potential failure point. The high number of wires and connections in the known system increases the likelihood of failure and spark and increases the difficulty in diagnosing failures. Additionally, current signals through the wires and cables generate electromagnetic fields that may cause electromagnetic interference problems with other nearby electronic devices.